The present invention relates to space and communications satellites, and more particularly, to a digital signal processing circuit for transmitting and receiving satellite communications.
There is a continually increasing demand for mobile satellite communications by users on the road, on the sea, and in the air. In order to continually expand mobile satellite service to broader markets, low cost mobile systems must be employed.
Current satellite technology directed towards the consumer market typically requires a tracking ground terminal. However, the tracking antennas with this current technology are expensive and bulky and, therefore, generally unacceptable to consumers.
These current conventional tracking ground terminals, include tracking arrays with mechanisms for steering beams, such as phase shifters and/or gimbals. These tracking arrays further include integrated mechanisms for tracking the pointing directions of beams, such as monopulse tracking loops, step scan, and open loop pointing schemes. In addition, for LEO or MEO constellation it is ultimately required to have an xe2x80x9cacquired before breakxe2x80x9d in the system. Therefore, multiple beams are required for user terminals. These conventional multibeam tracking phased arrays are too expensive for a consumer market, primarily because each beam has a separate set of electronics associated with each element to process the various signals, including many phase shifters and many duplicate strings of electronics. Therefore, the manufacturing costs for these conventional tracking phased arrays are generally beyond that practical for the consumer market whether for use as a fixed antenna or by a user as a mobile antenna.
It would therefore be desirable to reduce the complexity of the electronic circuitry associated with the mobile terminal.
It is an object of the present invention to provide a low profile mobile antenna terminal that employs signal processing circuitry that is reliable, cost effective and reduces the processing load.
In one aspect of the invention, a signal processing circuit for satellite communications signal includes a first one dimensional digital beam forming circuit for forming a beam signal in a first direction elevation and a second one dimensional digital beam forming circuit for forming a beam in a second direction. A direction (azimuth) filtering circuit is coupled between the first one dimensional digital beam forming circuit and the second one dimensional digital beam forming circuit to reduce the processing load on the second digital beam forming circuit by reducing the required processing bandwidth. The electronics circuit can form multiple beam with minimum overhead. The filtering circuit determining a communications signal direction of the satellite communications signal and tunes the filter to reduce a filter bandwidth and a frequency range of said beam signal prior to processing through the second one dimensional digital beam forming circuit.
In a further aspect of the invention, a method for signal processing a communications signals for a satellite comprises the steps of: receiving a signal from a satellite having a first frequency; reducing the bandwidth of the signal; forming first beam signal in a first direction; after the step of forming a fan beam, filtering the first beam signal to determine a beam direction signal; tuning the filter to reduce the dynamic frequency range in response to the beam direction signal; and forming spot beams in a second direction orthogonal to the first direction.
One advantage of the invention is that digital processing circuitry may be incorporated into the array to form multiple contiguous beams to allow automatic rough but cost effective direction tracking which is suitable for the mobile applications.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.